1. Field of the Invention
The present invention relates to a method of producing a semiconductor device comprising semiconductor layers containing silicon atoms, and more specifically, to a method of producing a semiconductor device comprising at least a p-type (or n-type) non-single crystal semiconductor layer containing silicon atoms, an i-type non-single crystal semiconductor layer containing silicon atoms, and an n-type (or p-type) non-single crystal semiconductor layer containing silicon atoms, wherein those semiconductor layers are arranged in the above-described order so as to form a pin structure, thereby forming a semiconductor device having photoelectric conversion capability such as a photovoltaic device, solar cell, photo detector, etc.
2. Description of the Related Art
It is well known that defects in semiconductor materials play important roles in generation and recombination of charges and strongly affect the mobility of carriers in the semiconductor materials. These defects cause degradation in the characteristics and performance of semiconductor devices.
One known compensation technique for defect levels arising from these defects is to perform hydrogen plasma treatment.
For example, U.S. Pat. No. 4,113,514 (J. I. Pankove et al.) discloses a technique in which a fabricated semiconductor device is subjected to hydrogen plasma treatment.
In the paper entitled "EFFECT OF PLASMA TREATMENT OF THE TCO ON a-Si SOLAR CELL PERFORMANCE" (F. Demichelis et. al., Mat. Res. Soc. Symp. Proc. Vol. 258, p. 905, 1992), there is disclosed a technique in which a pin-structure solar cell is formed on a transparent electrode deposited on a substrate wherein the transparent electrode on the substrate is subjected to hydrogen treatment before the formation of the pin-structure solar cell.
In a technique of fabricating a pin-structure solar cell, disclosed in the paper entitled "HYDROGEN-PLASMA REACTION FLUSHING FOR a-Si;H P-I-N SOLAR CELL FABRICATION" (Y. S. Tsuo et. al., Mat. Res. Soc. Symp. Proc. Vol. 149, p. 471, 1989), hydrogen treatment is performed on a p-type layer before the deposition of an i-type layer.
In the above hydrogen treatment techniques, hydrogen gas without any additional gas is introduced into a chamber evacuated to a low pressure, and the hydrogen gas is excited by discharging energy supplied for example by an RF (radio frequency) power source thereby exciting the hydrogen gas into a plasma state. Thus, a semiconductor device to be processed is exposed to the hydrogen gas plasma thereby performing hydrogen plasma treatment.
However, the hydrogen plasma not only acts to a portion to be processed such as a substrate or semiconductor layers on it but also expands to a wider region and attacks the inner wall of the chamber and a stage on which the semiconductor device to be processed is placed. Since the hydrogen plasma is in a very active state, it causes scattering of some atoms adsorbed on the surface of, or even residing in, the chamber wall or the stage. These atoms include unwanted impurities such as oxygen, nitrogen, carbon, iron, chromium, nickel, aluminum, etc., which may generate defect levels when incorporated into the semiconductor layer.
The surface of the semiconductor layer may be contaminated with these unwanted impurities, which results in degradation in characteristics of the semiconductor layer and thus the semiconductor device.
Compared with other gases used in film deposition processes, hydrogen is difficult to excite into a discharged state. In particular, in the case where a pure hydrogen gas is used, even if the hydrogen gas is successfully excited into a plasma state, it is difficult to maintain it. This means that it is difficult to perform stable hydrogen treatment.